import 'package:flutter/material.dart';

/// 自定义TabBar 指示器宽度
class MyUnderlineTabIndicator extends Decoration {


  const MyUnderlineTabIndicator({
    this.borderSide = const BorderSide(width: 2.0, color: Colors.white),
    this.insets = EdgeInsets.zero,
    this.wantWidth = 20
  });
  
  final double wantWidth;//传入的指示器宽度，默认20

  final BorderSide borderSide;

  final EdgeInsetsGeometry insets;

  @override
  Decoration? lerpFrom(Decoration? a, double t) {
    if (a is MyUnderlineTabIndicator) {
      return MyUnderlineTabIndicator(
        borderSide: BorderSide.lerp(a.borderSide, borderSide, t),
        insets: EdgeInsetsGeometry.lerp(a.insets, insets, t)!,
      );
    }
    return super.lerpFrom(a, t);
  }

  @override
  Decoration? lerpTo(Decoration? b, double t) {
    if (b is MyUnderlineTabIndicator) {
      return MyUnderlineTabIndicator(
        borderSide: BorderSide.lerp(borderSide, b.borderSide, t),
        insets: EdgeInsetsGeometry.lerp(insets, b.insets, t)!,
      );
    }
    return super.lerpTo(b, t);
  }

  @override
  _MyUnderlinePainter createBoxPainter([ VoidCallback? onChanged ]) {
    return _MyUnderlinePainter(this, wantWidth, onChanged);
  }

  Rect _indicatorRectFor(Rect rect, TextDirection textDirection) {
    final Rect indicator = insets.resolve(textDirection).deflateRect(rect);
    // return Rect.fromLTWH(
    //   indicator.left,
    //   indicator.bottom - borderSide.width,
    //   indicator.width,
    //   borderSide.width,
    // );
    double cw = (indicator.left + indicator.right) / 2;
    return Rect.fromLTWH(cw - wantWidth / 2,
        indicator.bottom - borderSide.width, wantWidth, borderSide.width);
  }

  @override
  Path getClipPath(Rect rect, TextDirection textDirection) {
    return Path()..addRect(_indicatorRectFor(rect, textDirection));
  }
}

class _MyUnderlinePainter extends BoxPainter {
  _MyUnderlinePainter(this.decoration, this.wantWidth, VoidCallback? onChanged);

  final MyUnderlineTabIndicator decoration;
  final double wantWidth;

  @override
  void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) {
    assert(configuration.size != null);
    final Rect rect = offset & configuration.size!;
    final TextDirection textDirection = configuration.textDirection!;
    final Rect indicator = decoration._indicatorRectFor(rect, textDirection).deflate(decoration.borderSide.width / 2.0);
    // final Paint paint = decoration.borderSide.toPaint()..strokeCap = StrokeCap.square;
    final Paint paint = decoration.borderSide.toPaint()..strokeCap = StrokeCap.round;
    canvas.drawLine(indicator.bottomLeft, indicator.bottomRight, paint);
  }
}
